Paul Williams was supposed to be fighting Kelly Pavlik tonight. But Pavlik – now scheduled to fight Miguel Espino on Dec. 19 – pulled out because of an injury to his left hand.

Pavlik is a very dangerous fighter when he’s right, what with 31 knockouts among his 35 victories. But there were no guarantees Pavlik would have been at his best against Williams.

Aside from the ongoing hand injury, many in the industry believe Pavlik has not psychologically recovered from his only loss – a one-sided affair against Bernard Hopkins in October 2008.

Consequently, few were giving Pavlik a chance to beat Williams, a 6-foot-3 lefty who has fought his way into top five pound-for-pound status.

Therefore, when some of the parties involved in tonight’s fight between Williams and Sergio Martinez say Williams is in for a tougher time with the southpaw from Argentina than he would have been against Pavlik, it might be true.

Williams (37-1, 27 KOs) and Martinez (44-1-2, 24 KOs) will square off in the middleweight main event at Boardwalk Hall in Atlantic City. Also on the card, Chris Arreola (27-1, 24 KOs) will take on journeyman Brian Minto (34-2, 21 KOs) in the heavyweight division.

Arreola was last seen being pummeled by champion Vitali Klitschko, who stopped Arreola after 10 rounds Sept. 26 at Staples Center.

Both fights will be televised by HBO.

Dan Goossen and Lou DiBella, respective promoters for Williams and Martinez, got into it during a recent conference call. DiBella took offense to Goossen saying this is a fight that will showcase the talented Williams to fans and the powers that be in Atlantic City, where Williams has yet to fight.

“I would like to take umbrage in what you just said, that this is a showcase for Paul Williams. … I think AC is looking for fighters like Paul, I agree with that,” DiBella said. “But more importantly, they are starving for great fights.

“Right here we have a great matchup and a very difficult fight for Paul and I’ve got to give Paul and his entire team credit for taking this fight because frankly it is a much more difficult fight than a Pavlik fight, with less reward.”

Goossen told DiBella he was not slighting Martinez.

“I have been telling everybody that Sergio Martinez is a much bigger risk in our eyes,” Goossen said. “On the other hand, we have so much confidence in Paul’s ability and we know that styles make fights. But Paul is different in that he takes control and makes everyone fight his fight.”

Martinez can fight. His only loss came to Antonio Margarito nearly 10 years ago.

In Martinez’s most recent start, he fought former welterweight champion Kermit Cintron to a majority draw with Martinez’s interim junior middleweight belt on the line.

One thing’s certain, Martinez is brimming with confidence.

“I am going to win by knockout and I am sure of it,” Martinez said. “I am in the best shape of my life at the best time of my career. I am a lot faster than Paul and I don’t take as many hits as he does, so that will really do well for me in this fight.”

Added DiBella: “Sergio has never lacked confidence, so he believes what he is saying, so maybe Paul is the one that is in trouble.”

Martinez is moving up from junior middleweight, and he said he will stay at middleweight if he can get a fight with Pavlik because “for sure, I will win against Williams.”

George Peterson, Williams’ trainer, almost laughed off Martinez’s cockiness.

“We are very confident about going in there and stopping this guy,” Peterson said.

“He has no pop and it is evident that Paul has a chin made of granite. We don’t know how long this guy is going to withstand this punishment.”

Williams, for one, likes Martinez’s frame of mind because it figures to make for a good fight.

“Well, they all talk like that until they get in the ring when the bell rings,” Williams said, “and they start taking all the punches I’m throwing. I am glad his confidence is such as that. We will have a fight.”

As for Arreola-Minto, Arreola is fighting just 10 weeks after absorbing tremendous punishment from Klitschko. During a recent interview with this newspaper, Arreola assured us he is mentally ready to get back at it.

“I’m over it,” he said.

But did he learn anything from the loss? Goossen, who also promotes Arreola, said Arreola “cut corners” while training for Klitschko.

“To be brutally honest, I know he did,” Goossen said.

Not so, Arreola said.

“I didn’t cut corners,” Arreola said. “The missed days, I missed them because I was sick. There is no reason to go to train and half-ass training. When you hit the bag hit you the bag like you’re going to fight, or you don’t hit it at all.